Kinetoplastid protozoa include early-branched species of trypanosomes that cause large amounts of disease worldwide. They exhibit a unique form of RNA editing by the specific insertion and deletion of uridylates in most mitochondrial mRNAs prior to their translation. An array of proteins in a complex, termed the "editosome", catalyze this editing whose substrate specificity is differentially regulated during development. It is reasonable to speculate that a battery of accessory factors regulates this process via transient interactions with editing proteins and specific RNA substrates, however these factors and their mode of action remain poorly understood. We submit that this explorative /developmental R21 research proposal will break new ground and extend the current state of the art in the field toward new directions;namely, the elucidation of regulatory mechanisms of T. brucei U-insertion/deletion RNA editing. It focuses on a novel DExH-box helicase (termed here REH2;RNA editing-associated helicase 2) that we showed is functionally linked to RNA editing in vivo, co-purifies with a known accessory factor of editing and forms a novel mitochondrial ribonucleoprotein complex we initially characterized here ("mtREH2c"). Importantly, RNA editing complexes and mtREH2c are independent particles although at least REH2 transiently binds editing proteins and enzymatic activities in an RNA-independent fashion. We propose to define: (Aim 1) The functional relationship of REH2 and other putative cofactors of mtREH2c with RNA editing in vivo, and (Aim 2) The protein composition of mtREH2c. To our knowledge, REH2 in trypanosomes and Suv3p in yeast (and orthologues) are the only mitochondrial DExH-box helicases currently under study. PUBLIC HEALTH RELEVANCE: Kinetoplastids are responsible for several extensive diseases including sleeping sickness, leishmaniasis and chagas disease. Understanding a unique form of RNA editing in these pathogens, particularly the molecular basis of its regulation during the life cycle, may provide information important for therapeutic and preventative treatments. The current proposal addresses a novel regulatory enzyme in this RNA editing.